The present invention relates to a method of detecting the alignment of printheads relative to one another in an ink jet printer having a plurality of printheads arranged side-by-side in a first direction on a carriage, each print head having a conductive nozzle plate which defines an edge that extends in said first direction, wherein a sensor is used for determining the position of a reference mark formed on the print head. The present invention also relates to a printer for applying the present method.
A printer, e.g., an ink jet printer, comprises one or more print heads each of which carries an array of print elements, e.g., nozzles, for printing pixels on a sheet of a print substrate that is moved along a predetermined path relative to the print head. Typically, the print heads are mounted on a carriage that is moved across the path of the substrate in a main scanning direction Y, whereas the substrate is advanced in a sub-scanning direction X. The print elements or nozzles typically form a linear array that extends in X-direction.
In order to obtain a high quality of the printed image, the nozzles on the print heads must be positioned or positionable with high accuracy relative to the substrate. For example, in the typical set-up described above, the linear array of nozzles should form a specified angle with the main scanning direction Y, typically an angle of exactly 90°. Moreover, when a plurality of print heads are employed, for example, print heads for different colours, the print heads must be precisely aligned relative to one another in at least one direction, typically the sub-scanning direction X. In the other direction Y, it is at least required that the relative positions of the print heads and hence the nozzles are known with high accuracy, so that the individual print elements can be energised at correct timings in accordance with the image information.
A conventional method of detecting the alignment of the print heads consist of printing a test pattern which may then be inspected visually.
U.S. Pat. Nos. 6,371,591 B1 and 6,508,530 B1 disclose automatic detection methods of the type indicated above, utilising opto-electronic sensors.
U.S. Pat. No. 4,941,405 discloses a capacitive measurement of the position of the carriage in the main scanning direction, for controlling the timings at which the print elements are filed.
U.S. Pat. No. 6,498,685 discloses a capacitive system for detecting the two-dimensional alignment of a printhead (an optical exposure system) in a lithography system. Here, the individual printheads are aligned relative to the wafer which corresponds to the print substrate. The capacitive detection method relies upon a periodic pattern formed on the wafer.
US-A-2003 0 0085 938 discloses a capacitive measurement system for measuring an alignment of two substrates which, together, form the printhead. This system is used only when the printhead is assembled.